Other contenders don't come close: Former Sen. Jim Webb (D-Virginia) had just 2% and former Maryland Gov. Martin O'Malley (D) had 1%.

But Biden's number is particularly striking as he is not yet a candidate.

Recent photos of Joe Biden as he mulls his presidential run:

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Joe Biden as he mulls over a presidential run

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Joe Biden just got some good news in a new poll

NEW YORK - SEPTEMBER 10: Stephen talks with Vice President Joe Biden, on The Late Show with Stephen Colbert, Thursday Sept 10, 2015 on the CBS Television Network. (Photo by Jeffrey R. Staab/CBS via Getty Images)

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The vice president, reeling from the death of his son, has repeatedly said he is not sure if he is emotionally ready for what would undoubtedly be a grueling campaign.

"We're just not quite there yet. And [we] may not get there in time to make it feasible to be able to run and succeed because there's certain windows that will close. But if that's it, that's it. But it's not like I can rush it," Biden told the Catholic magazine America in an interview published Monday. "I know that's not satisfying to anybody."

The Bloomberg poll also comes as Clinton's campaign tries to stabilize itself after a rocky summer filled with critical headlines about her use of a private email server at the State Department. She has recently shifted tactics as a result, conducting regular interviews and trying to show more humor on the campaign trail.

Since the last Bloomberg survey in April, Clinton has suffered a 10-point drop in her favorability ratings, from 48% to 38%, while Biden has had a 3-point uptick, from 46% to 49%.

"He was the only one of a dozen national political figures and entities whose approval rating improved over the summer," Bloomberg reported.